1. Field of the Invention
The invention pertains to a self-pumping hydropneumatic suspension strut unit with internal level control, with an oil-filled working cylinder subject to the pressure of gas cushions and with a damping piston, which is free to slide inside the cylinder and is mounted at the end of a hollow piston rod, the cavity of which serves as a pump cylinder for a pump rod attached to the working cylinder. Oil is drawn from a reservoir space when the piston rod travels outward, whereas the oil is conveyed into the working space when the piston rod travels inward. The pump rod passes through the end wall of the working space and is held axially in position by an end-mounted disk, which acts as a universal joint for the rod. The disk engages in a groove in the pump rod and is held in place by its outer circumference axially between the working cylinder and the end wall of the working cylinder.
2. Description of the Related Art
Self-pumping hydropneumatic suspension strut units with internal level control according to the introductory clause are already known (e.g., DE 33 18 939 C2). The pump rod has here a circumferential groove, and a slotted disk engages in this groove to hold the pump rod in place with respect to the working space. The pretensioning force of the working cylinder exerts a clamping force, which fixes the pump rod axially in place. During operation of a suspension strut unit of this type, it has been found that changes in the overall length of the unit occur as a result of fluctuations in temperature and pressure. As a result of such changes, the working cylinder can lose its pretensioning force, and the slotted disk, because of the lack of elasticity of the associated components, can work itself loose. The disadvantage here is not only that noise can develop but also that, under certain conditions, a decrease in the damping pressure can occur in the suspension spring strut unit.